Gas turbine combustor

ABSTRACT

A gas turbine combustor is provided with a nozzle extension tube having an inclination outward in a diameter direction of a combustor inner cylinder and in a peripheral direction of the combustor inner cylinder. As a result, the premixed gas is transformed to a spiral flow passing into a combustion chamber while turning, i.e., an outward turning flow, thereby sufficiently mixing the premixed gas while the premixed gas is flowing in the combustion chamber.

FIELD OF THE INVENTION

[0001] This invention relates to a gas turbine. More specifically, thisinvention relates to a gas turbine combustor which can reduce thegeneration of NO_(x) during the operation of the gas turbine.

BACKGROUND OF THE INVENTION

[0002] A diffusion combustion system, in which fuel and the air areejected from different nozzles and burned, has been often used forconventional gas turbine combustors. Recently, however, a premixcombustion system which is more advantageous in the reduction of thermalNO_(x) has been also used inplace of the diffusion combustion system.The premix combustion system means that fuel and the air are premixedwith each other and the mixture is ejected from the same nozzle andburned. According to this combustion system, even if fuel is rarefied,it is possible to burn the fuel in that state in any combustion regions.Therefore, it is easy to decrease the temperature of the premixed fuel,and this premix combustion system is advantageous in the reduction ofNO_(x), as compared with the diffusion combustion system. On the otherhand, this premix combustion system has the following problem, that is,the stability of a combustion state is inferior because the air isexcess with respect to the fuel and the temperature of premixed flamesis low.

[0003]FIG. 16 is a front view which shows one example of a premix typegas turbine combustor. A combustor inner cylinder 20 is provided in acombustor outer casing 10 at a constant clearance kept between thecylinder and the casing. A diffusion flame formation cone 30 which formsdiffusion flames is provided on the central portion of the combustorinner cylinder 20. The diffusion flame formation cone 30 causes pilotfuel supplied from a pilot fuel supply nozzle 31 to react with the airsupplied from the portion between the combustor outer casing 10 and thecombustor inner cylinder 20, and forms diffusion flames.

[0004] Although it is not clear from FIG. 16, eight premixed flameformation nozzles 40 which form premixed flames are provided around thediffusion flame formation cone 30. Premixed gas is formed by mixing theair supplied from the portion between the combustor outer casing 10 andthe combustor inner cylinder 20 with main fuel and then ejected from thepremixed flame formation nozzles 40. The premixed gas ejected from thepremixed flame formation nozzles 40 is passed through premixed flameformation nozzle extension tubes 400 provided at the outlets of thenozzles 40, respectively and ejected toward a combustion chamber 50.This premixed gas is ignited by high-temperature combustion gasdischarged from the diffusion flames and forms premixed flames.High-temperature, high-pressure combustion gas is discharged from thepremixed flames, passed through a combustor tail pipe (not shown) andthen introduced into the first stage nozzle of a turbine.

[0005] In the meantime, in the gas turbine combustor, the premixed gasis ejected linearly from the premixed flame formation nozzle extensiontubes 400 toward the combustion chamber50, and therefore uneven fuelconcentration portions exist in the premixed gas. Therefore, combustiontemperature is high on the portions of the premixed gas on which thefuel concentration is high and NO_(x) tends to be generated on theportions. To solve this problem and to suppress further generation ofNO_(x) in the premix type gas turbine combustor, it is necessary tosufficiently mix the main fuel with combustion air. From this viewpoint,Japanese Patent Application Laid-Open (JP-A) No. 7-248118 discloses apremix combustor which is provided with a premix unit consisting of agroup of cylindrical members which generate turning flows of thecombustion air in a premix combustor. In addition, JP-A No. 8-28871discloses a gas turbine combustor which is provided with units whichrespectively turn premixed gas in a peripheral direction so that aplurality of turning flows of the premixed gas are wound around oneanother or twisted into one another in the combustor.

[0006] However, in each of the gas turbine combustors disclosed in theJP-A Nos. 7-248118 and 8-28871, the premixed gas is transformed toturning flows directing inward in the direction of the center of acombustion chamber and twisted, and thereby a combustion gas recycleregion cannot be sufficiently formed. Therefore, these gas turbinecombustors have disadvantages in that the flame holding of the premixedflames become unstable and stable combustion cannot be thereby obtainedand that oscillating combustion and the like are caused. Further, sincethe premixed gas is concentrated in the neighborhood of the center ofthe combustion chamber and combusted, local high-temperature portionstend to be generated and the generation of NO_(x) cannot be sufficientlysuppressed.

SUMMARY OF THE INVENTION

[0007] It is an object of this invention to provide a gas turbinecombustor which can reduce the generation of NO_(x) during the operationof a gas turbine and which can stably combust gas.

[0008] The gas turbine combustor according to one aspect of thisinvention comprises a combustor inner cylinder, and a diffusion flameformation cone which is disposed inside of the combustor inner cylinderand which forms diffusion flames by mixing pilot fuel with air. The gasturbine combustor also comprises a premixed flame formation nozzle whichis provided annularly between the combustor inner cylinder and a pilotflame formation cone and which forms premixed flames out of premixed gasformed by mixing main fuel with the air. The gas turbine combustorfurther comprises a premixed flame formation nozzle extension sectionwhich is disposed at an outlet of the premixed flame formation nozzleand which forms a flow of premixed gas turning in a peripheral directionof the combustor inner cylinder while being directing outward in adiameter direction of the combustor inner cylinder.

[0009] The gas turbine combustor according to another aspect of thisinvention comprises a combustor inner cylinder, and a diffusion flameformation cone which is disposed inside of the combustor inner cylinderand which forms diffusion flames by mixing pilot fuel with air. The gasturbine combustor also comprises a premixed flame formation nozzle whichis provided annularly between the combustor inner cylinder and a pilotflame formation cone and which forms premixed flames out of premixed gasformed by mixing main fuel with the air. The gas turbine combustorfurther comprises a premixed flame formation nozzle extension sectionwhich is disposed at an outlet of the premixed flame formation nozzlewhile being inclined outward in a diameter direction of the combustorinner cylinder and inaperipheral direction of the combustor innercylinder with respect to an axial direction of the combustor innercylinder, and which ejects premixed gas formed at the premixed flameformation nozzle.

[0010] The gas turbine combustor according to still another aspect ofthis invention comprises a combustor inner cylinder, and a mixed gasformation cylinder which has a nozzle ejecting pilot fuel and a nozzleejecting main fuel and which is disposed inside of the mixed gasformation cylinder. The gas turbine combustor also comprises a mixed gasejection extension section which is disposed at an outlet of the mixedgas formation cylinder while being inclined outward in a diameterdirection of the combustor inner cylinder and in a peripheral directionof the combustor inner cylinder with respect to an axial direction ofthe combustor inner cylinder, and which ejects gas formed by mixing thepilot fuel with air and premixed gas formed by mixing the main fuel withthe air.

[0011] Other objects and features of this invention will become apparentfrom the following description with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a front view of a gas turbine combustor according to afirst embodiment of the invention,

[0013]FIG. 2 is a cross-sectional view of the gas turbine combustorshown in FIG. 1, taken along an axial direction thereof,

[0014]FIG. 3A and FIG. 3B show cross-sectional views of a premixed flameformation nozzle extension tube used in the first embodiment, takenalong an axial direction thereof,

[0015]FIG. 4 is a side view of a main fuel supply nozzle, FIG. 5A is across-sectional view of a combustor inner cylinder to which a coolingunit is attached, taken along an axial direction thereof, and FIG. 5B isa perspective view of the cooling unit,

[0016]FIG. 6 is a front view of the first modification of the gasturbine combustor according to the first embodiment of the invention,

[0017]FIG. 7 is a front view of the second modification of the gasturbine combustor according to the first embodiment of the invention,

[0018]FIG. 8 is a front view of a gas turbine combustor according to asecond embodiment of the invention,

[0019]FIG. 9 is a cross-sectional view of the gas turbine combustorshown in FIG. 8, taken along an axial direction thereof,

[0020]FIG. 10 is a cross-sectional view of a mixed gas formationcylinder used in the second embodiment, taken along an axial directionthereof,

[0021]FIG. 11 is a front view of a gas turbine combustor according to athird embodiment of the invention,

[0022]FIG. 12 is a front view of a gas turbine combustor according to afourth embodiment of the invention,

[0023]FIG. 13 is a cross-sectional view of a nozzle extension tube usingthe gas turbine combustor according to the fourth embodiment,

[0024]FIG. 14 is a front view of a gas turbine combustor according tothe modification of the fourth embodiment,

[0025]FIG. 15 is a cross-sectional view of anozzle extension tube usedin the fourth embodiment, and

[0026]FIG. 16 is a front view which shows one example of a premix typegas turbine combustor.

DETAILED DESCRIPTIONS

[0027] This invention will be described hereinafter in detail withreference to the drawings. It is noted that this invention should not belimited to the following embodiments. It is also noted that constituentelements in the embodiments to be described below include those which aperson skilled in the art can easily assume.

[0028] A first embodiment of this invention will be explained below. Inthe first embodiment, this invention will be explained while taking up acase of attaching a premixed flame formation nozzle extension tube orthe like to each premixed flame formation nozzle or the like andejecting premixed gas toward a combustion chamber as an example. It isnoted that a premixed flame formation nozzle extension section and amixed gas ejection extension section according to this invention includenot only a premixed flame formation nozzle extension tube or the likebut also a case of extending the outlet of each premixed flame formationnozzle or the like to directly eject premixed gas or the like toward acombustion chamber.

[0029]FIG. 1 is a front view of a gas turbine combustor according to thefirst embodiment. FIG. 2 is a cross-sectional view of the gas turbinecombustor shown in FIG. 1, taken along an axial direction thereof. FIG.3A and FIG. 3B show cross-sectional views of a premixed flameformationnozzle extension tube used in the first embodiment, taken alongan axial direction thereof. As shown in FIG. 1 and FIG. 2, the diffusionflame formation cone 30 is provided inside of the combustor innercylinder 20. The pilot fuel supply nozzle 31 which ejects pilot fuel isprovided inside of this diffusion flame formation cone 30. The pilotfuel ejected from the pilot fuel supply nozzle 31 reacts with thecombustion air and diffusion flames are formed. A swirler 33 whichagitates the combustion air is provided around the pilot fuel supplynozzle 31 to sufficiently mix the combustion air with the pilot fuel.The diffusion flame formation cone 30 ejects mixture gas of thecombustion air and the pilot fuel toward a combustion chamber 50 (seeFIG. 2) and forms diffused combustion flames.

[0030] As shown in FIG. 2, premixed flame formation nozzles 40 arearranged between the combustor inner cylinder 20 and the diffusion flameformation cone 30 which forms the diffused combustion flames. Althoughit is not clear from FIG. 2, the eight premixed flame formation nozzles40 are arranged annularly around the diffusion flame formation cone 30.It is noted that the number of the premixed flame formation nozzles 40is not limited to eight but may be appropriately changed according tothe specification of a gas turbine combustor. In addition, as shown inFIG. 1 and FIG. 2, premixed flame formation nozzle extension tubes (tobe simply referred to as “nozzle extension tubes” hereinafter) 410serving as premixed flame formation nozzle extension sections areprovided at the respective outlets of the premixed flame formationnozzles 40. Premixed gas is ejected through the nozzle extension tubes410 toward the combustion chamber 50.

[0031] As shown in FIG. 1, the outlets of the nozzle extension tubes 410are sector-shaped. If so shaped, the clearances between the adjacentnozzle extension tubes 410 are kept almost constant and the air therebyflows evenly from the adjacent nozzle extension tubes 410. Therefore, itis possible to suppress high-temperature combustion gas from flowingback to the portions on which the air flows weakly, making it possibleto reduce the burning of the portions on which the nozzle extensiontubes 410 are adjacent each other. Further, the air flows almost evenlyfrom the portions between the adjacent nozzle extension tubes 410, thosebetween the nozzle extension tubes 410 and the combustor inner cylinder20, and those between the nozzle extension tubes 410 and the diffusionflame formation cone 30. It is, therefore, possible to suppressflashback caused by uneven air flows and to thereby reduce the burningof the nozzle extension tubes 410 and the like.

[0032] In each of the nozzle extension tubes 410, among sides of thenozzle extension tube 410 existing in the diameter direction of thecombustor inner cylinder 20, at least a side 411 close to the centralaxis of the combustor inner cylinder 20 is inclined, at a certain anglea with respect to a plane perpendicular to the central axis of thecombustor inner cylinder 20, outward in the diameter direction of thecombustor inner cylinder (FIG. 3A). Furthermore, as shown in FIG. 3B, aside 412 of the nozzle extension tube 410 existing in the peripheraldirection of the combustor inner cylinder 20 is inclined, at a certainangle β with respect to the plane perpendicular to the central axis ofthe combustor inner cylinder 20, in the peripheral direction of thecombustor inner tube 20.

[0033] In this way, by inclining the nozzle extension tube 410 outwardin the diameter direction of the combustor inner cylinder 20, it ispossible to transform the premixed gas to an outward flow (as indicatedby an arrow A shown in FIG. 3A). Further, by inclining the nozzleextension tube 410 in the peripheral direction of the combustor innercylinder 20, it is possible to give the premixed gas turning in theperipheral direction of the combustor inner cylinder 20 (as indicated byan arrow B shown in FIG. 3B). It is noted that optimum values can beappropriately selected for the angles α and β, respectively according tothe specification of the combustor. However, if the both angles are toosharp, the mixture of the premixed gas becomes insufficient, making itdifficult to suppress NO_(x). Conversely, ifthebothangles are too wide,the premixed gas tends to remain in the combustion chamber and flashbackmay possibly occur. Therefore, with a view of effectively forming arecycle region to reduce NO_(x) and decreasing the probability offlashback, it is preferable that both the angles α and β are set withina range of 20 to 50 degrees. In addition, with a view of forming aneffective recycle region while minimizing the pressure loss of thenozzle extension tube 410 as much as possible, it is preferable that theboth angles α and β are set within a range of 30 to 40 degrees.

[0034] The gas turbine combustor will next be described with referenceto FIG. 2. The air fed from a compressor (not shown) is introduced intoan internal portion of the combustor outer casing 10, passed through theportion between the combustor outer casing 10 and the combustor innercylinder 20 and then changes its traveling direction by 180 degrees.Thereafter, the air is fed to the premixed flame formation nozzles 40and the diffusion flame formation nozzle 32 from the backward of thecombustor inner cylinder 20 and mixed with main fuel and pilot fuel,respectively.

[0035] The compressed air introduced into the diffusion flame formationnozzle 32 is agitated by the swirler 33 provided in the diffusion flameformation nozzle 32 and sufficiently mixed with the pilot fuel ejectedfrom a pilot fuel supply nozzle 31. The mixture gas of the pilot fueland the compressed air forms diffusion flames and the diffusion flamesare ejected from the diffusion flame formation cone 30 toward thecombustion chamber 50. The diffusion flames promptly combust premixedgas formed by the premixed flame formation nozzles 40. In addition, thediffusion flames stabilize the combustion of the premixed gas andsuppress the flashback of premixed flames and the self ignition of thepremixed gas.

[0036] The compressed air introduced into the premixed flame formationnozzles 40 is agitated by a swirler 42 provided in each of the premixedflame formation nozzles 40. The main fuel ejected from main fuel supplyholes 61 provided in a main fuel supply nozzle 60 is sufficiently mixedwith the compressed air to form premixed gas. After the formation of thepremixed gas, the premixed gas is ejected from the nozzle extensiontubes 410 toward the combustion chamber 50. Since it is necessary tosuppress the generation of NO_(x), the premixed gas contains excessiveair relative to the fuel. This premixed gas is promptly ignited byhigh-temperature combustion gas discharged from the diffusion flames,premixed flames are formed, and high-temperature, high-pressurecombustion gas is discharged from the premixed flames.

[0037] As described above, at least the side 411 of each nozzleextension tube 410 which is close to the central axis of the combustorinner cylinder 20 is inclined, at the certain angle a with respect tothe axial direction of the combustor inner cylinder 20, toward the innerwall of the combustor inner cylinder 20. In addition, the outlet of eachnozzle extension tube 410 is inclined at the certain angle β withrespect to the axial direction of the combustor inner cylinder 20.Therefore, the combustion gas in the combustion chamber 50 istransformed to a flow which travels spirally around the axis of thecombustor inner cylinder 20, so-called an outward turning flow.

[0038] The main fuel supply nozzle 60 will now be described. FIG. 4 is aside view of the main fuel supply nozzle 60. A plurality of spokes 62each having a sector-shaped cross section in a peripheral directionthereof is provided around the main fuel supply nozzle 60. In addition,two main fuel supply holes 61 which eject the main fuel are provided oneach side surface of the spoke 62, four main fuel supply holes 61 intotal are provided on the both side surfaces thereof. It is noted thatif the diameter of each main fuel supply hole 61 becomes small, thenumber of the holes 61 increases. In addition, if the diameter of themain fuel supply hole 61 is set too small, the ejection of the main fuelbecome unstable. Therefore, although the number of the main fuel supplyholes 61 should not be limited to four, it is preferable to set thenumber so that the diameter of the hole 61 is in a range in which themain fuel can be stably ejected. The number of themain fuel supplyholes61 depends on the diameter of each main fuel supply hole 61, but one tofour, preferably two or three main fuel supply holes 61 are provided oneach side surface of the spoke 62.

[0039] The cross section of this spoke 62 has been conventionallycircular-shaped. However, with such a cross-sectional shape, a vortex orthe peel-away of the air occurs to the backward of the spoke 62. Thiscauses the generation of flashback. If the cross section has a sectorshape as that of the spoke 62 in this embodiment, the air smoothly flowsaround the spokes 62 and the disturbance of the air can be suppressed inthe backward of the spokes 62, thereby making it possible to suppressflashback. This can reduce the burning of the nozzle extension tubes andthe like and, therefore, lengthen the life of the combustor. Besides, itis possible to reduce the labor of maintenance.

[0040] The cooling of the combustor inner cylinder 20 will next bedescribed. FIG. 5A is a cross-sectional view of the combustor innercylinder to which a cooling unit is attached, taken in an axialdirection thereof. Since the flow of the combustion gas in the gasturbine combustor of the present invention is an outward turning flow,the combustion gas and the premixed flames are struck against thecombustor inner cylinder 20 a on the combustion chamber 50 side (asindicated by an arrow C shown in FIG. 5A). Therefore, the portion of thecombustor inner cylinder 20 a on the combustion chamber 50 side againstwhich the combustion gas and the like are struck, becomes high intemperature, which sometimes shorten the life of this portion.

[0041] To avoid this disadvantage, it is preferable that the coolingunit is provided around the combustor inner cylinder 20 a on thecombustion chamber 50 side so as to remove the heat of the combustiongas and the like. In the example shown in FIG. 5A, the combustor innercylinder 20 a on the combustion chamber 50 side is formed with platefins 21 to provide the cooling unit. The structure of the plate fin 21is shown in FIG. 5B. First, the air from the compressor which has beenpassed through the portion between the combustor outer casing 10 and thecombustor inner cylinder 20, flows into each plate fin 21 throughcooling air holes 21 a (see FIG. 5B) provided in the plate fin 21 on theouter casing 10 side. This air cools the combustor inner cylinder 20 aon the combustion chamber 50 side by convection cooling when the airflows into the plate fins 21. In addition, the air that has flowedthrough the plate fins 21 flows out toward the combustion chamber 50 (asindicated by an arrow J direction shown in FIG. A). By flowing along thesurface of the combustion inner cylinder 20 a on the combustion chamber50 side, this air forms a thermal boundary layer in the neighborhood ofthe surface of the combustion inner cylinder 20 a and film-cools thecombustor inner cylinder 20 on the combustion chamber 50 side.

[0042] It is noted that the cooling unit should not be limited to theplate fins 21 but fins called MT fins may be used or holes may beprovided around the combustor inner cylinder 20 a on the combustionchamber 50 side so that cooling air is ejected from the holes to therebyfilm-cool the combustor inner cylinder 20 a on the combustion chamber 50side. According to such a cooling unit, even if the high-temperaturecombustion gas and the like are struck against the surface of the innercylinder on the combustion chamber 50 side, the portion is cooled.Therefore, it is possible to suppress a local temperature rise of thecombustor inner cylinder 20 a on the combustion chamber 50 side.Accordingly, it is possible to form an outward flow more actively, andtherefore the mixture of premixed gas can be further accelerated.

[0043] Since the combustion gas in the conventional gas turbinecombustor forms an inward, twisted turning flow that turns toward thecenter of the combustor, premixed gas is concentrated in theneighborhood of the center of the combustion chamber 50. As a result,combustion is accelerated on this portion, local high-temperatureportions tend to be generated, and the generation of NO_(x) cannot besuppressed sufficiently. Furthermore, since the recycle region cannot besufficiently formed in the neighborhood of the center of the combustionchamber 50, the premixed gas becomes unstable to cause oscillatingcombustion and the like.

[0044] According to the gas turbine combustor of the present invention,by contrast, each nozzle extension tube is given certain angle, therebygiving the premixed gas a flow directing outward in the diameterdirection of the combustor inner cylinder 20 and turning in theperipheral direction thereof, i.e., an outward turning flow. Therefore,the premixed gas is evenly combusted over the entire regions of thecombustion chamber 50 while being sufficiently mixed in the course ofthe flow of surrounding the diffusion flames. As a result, localhigh-temperature portions less occur and the generation of NO_(x) can besuppressed sufficiently. Furthermore, since the recycle region formed onthe central portion of the combustor is widened by the outward turningflow, the premixed flames are stably formed and oscillating combustioncan be suppressed. In addition, since the premixed gas is combusted overthe entire regions of the combustion chamber 50, there hardly remainshalf-burned premixed gas, making it possible to effectively use thefuel. In this embodiment, the outlet of each nozzle extension tube 410is simply inclined outward in the diameter direction of the combustorinner cylinder 20 and in the peripheral direction thereof so as to formthe outward turning flow, and therefore it is not necessary to speciallywork the interior of the outlet of each nozzle extension tube 410,facilitating the manufacturing of the combustor.

[0045] A first modification of the first embodiment will be describedbelow. FIG. 6 is a front view of the first modification of the gasturbine combustor according to the first embodiment. In the gas turbinecombustor according to the first embodiment, the outlet of each nozzleextension tube 410 (see FIG. 1) is sector-shaped. It is also possible toform the outlet of each nozzle extension tube 420 to be elliptic as seenin this modification. Even with the elliptic outlet thereof, thepremixed gas ejected from each nozzle extension tube 420 forms anoutward turning flow. Therefore, it is possible to combust the gas overthe entire combustion chamber (not shown) to decrease localhigh-temperature portions and to suppress the generation of NO_(x). Inthis modification, it is also possible to form the outlet of each nozzleextension tube 420 to be circular.

[0046]FIG. 7 is a front view of a second modification of the gas turbinecombustor according to the first embodiment. As seen in thismodification, nozzle extension tubes 430 directing outward and nozzleextension tubes 420 forming outward turning flows may be alternatelyarranged. If the nozzle extension tubes are thus arranged, the outwardstraight flows of the premixed gas formed by the nozzle extension tubes430 are struck against the outward turning flows of the premixed gasformed by the nozzle extension tubes 420 to advantageously acceleratethe mixture of the premixed gas. It is noted that the outlet shape ofeach of the nozzle extension tubes 430 and 420 is not limited to theelliptical shape shown in FIG. 7 but may be a sector shape or a circularshape as shown in FIG. 1.

[0047]FIG. 8 is a front view of a gas turbine combustor according to asecond embodiment of the invention. FIG. 9 is a cross-sectional view ofthe gas turbine combustor shown in FIG. 8, taken along an axialdirection thereof. In addition, FIG. 10 is a cross-sectional view of amixed gas formation cylinder used in the second embodiment, taken alongan axial direction thereof. The gas turbine combustor according to thisembodiment provides spokes 63 having main fuel supply holes 64 formedtherein which supply main fuel into mixed gas formation cylinders 70 andpilot nozzles 36 and by arranging the mixed gas formation cylinders 70annularly inside of the combustor inner cylinder 20.

[0048] Each of the mixed gas formation cylinders 70 used in thisembodiment includes the main fuel supply holes 64 which eject the mainfuel into the cylinders 70, respectively and pilot nozzles 36 eachhaving a pilot fuel supply nozzle 35 provided therein as shown in FIG.10. In addition, a swirler 72 is provided on the air intake port side ofeach mixed gas formation cylinder 70 to turn compressed air forcombustion and sufficiently mix the compressed air with the main fueland the pilot fuel.

[0049] A nozzle extension tube 440 which serves as a mixed gas ejectionextension section is provided on the outlet side of each of the mixedgas formation cylinder 70. This nozzle extension tube 440 ejects gas inwhich the combustion compressed air is mixed with the main fuel and thepilot fuel, toward a combustion chamber 50. The outlet of each nozzleextension tube 440 is circular-shaped and inclined outward in thediameter direction of the combustor inner cylinder 20. The nozzleextension tube 440 is also inclined in the peripheral direction of thecombustion inner cylinder 20. It is noted that the outlet shape of eachnozzle extension tube 440 is not limited to the circular shape but maybe the sector shape or the elliptic shape as shown in the firstembodiment. The same thing is true hereinafter.

[0050] In the gas turbine combustor in this embodiment, five mixed gasformation cylinders 70 each having the nozzle extension tube 440provided on the outlet thereof are arranged annularly inside of thecombustor inner cylinder 20 (see FIG. 8 and FIG. 9). It is noted thatthe number of the mixed gas formation cylinders 70 is not limited tofive but may be appropriately changed according to the specification ofa gas turbine combustor and the like.

[0051] The gas turbine combustor in this embodiment will be describedwith reference to FIG. 9. The compressed air for combustion fed from acompressor (not shown) is introduced into a combustor outer casing 10,passed through the portion between the combustor outer casing 10 and thecombustor inner cylinder 20 and then changes its traveling direction by180 degrees. The combustion compressed air is introduced into the pilotnozzles 36 and the mixed air formation cylinders 70 from the backward ofthe mixed gas formation cylinders 70.

[0052] The gas turbine combustor will be described with reference toFIG. 10. The compressed air introduced into each pilot nozzle 36 issufficiently mixed with the pilot fuel ejected from the pilot fuelsupply nozzle 35. In addition, after the air introduced into each mixedgas formation tube 70 is agitated by the swirler 72 provided in eachmixed gas formation cylinder 70, the air is sufficiently mixed with themain fuel ejected from the main fuel supply holes 64 and premixed gas isformed. It is noted that the air is excess relative to the fuel in thepremixed gas so as to suppress the generation of NO_(x). In addition,from the viewpoint of suppressing flashback, the spokes each having asector-shaped cross section described in the first embodiment arepreferably used as the spokes 63 provided with the main fuel supplyholes 64. If using them, it is possible to effectively suppress theflashback and to thereby suppress the burning of the nozzle extensiontubes 440 and the like. In addition, since the combustion is stabilized,it is also possible to suppress oscillating combustion.

[0053] The mixed gas and the premixed gas formed out of the pilot fueland the compressed air are ejected through the nozzle extension tubes440 toward the combustion chamber 50. The mixed gas of the pilot fueland the compressed air ejected toward the combustion chamber 50 formsdiffusion flames, and high-temperature combustion gas generated from thediffusion flames promptly combusts the premixed gas. Thehigh-temperature combustion gas also stabilizes the combustion of thepremixed gas to thereby suppress the generation of the flashback of thepremixed flames and the self ignition of the premixed gas. The combustedpremixed gas forms premixed flames, and high-temperature, high-pressurecombustion gas is discharged from the premixed flames.

[0054] The mixed gas and the premixed gas formed by mixing the pilotfuel with the compressed air are transformed to outward turning flowsdirecting outward in the diameter direction of the combustor innercylinder 20 and turning in the peripheral direction thereof by thenozzle extension tubes 440, and the flows pass into the combustionchamber 50. The outward turning flows enable the premixed gas and thelike to be combusted over the entire regions of the combustor whilesufficiently mixing the premixed gas and the like. Therefore, localhigh-temperature portions are reduced and the generation of NO_(x) issuppressed. Further, because of the outward turning flows, pressure ishigh in the neighborhood of the inner wall of the combustion chamber 50and low in the neighborhood of the center thereof. As a result, acirculating flow is generated between the neighborhood of the inner walland the neighborhood of the center, thereby forming a recycle region.Consequently, the flames are stabilized and oscillating combustion isdecreased, making it possible to ensure the stable operation of thecombustor. As described in the first embodiment, a cooling unit may beprovided at the combustor inner cylinder on the combustion chamber 50side so as to cool the portion of the combustor inner cylinder againstwhich flames formed by combusting high-temperature combustion gas andmixed gas are struck. By doing so, it is possible to form the outwardturning flows more actively. Therefore, the fuel is mixed with the airmore sufficiently and evenly combusted, making it possible to suppressthe generation of local high-temperature portions. As a result, thegeneration of NO_(x) can be further suppressed.

[0055]FIG. 11 is a front view of a gas turbine combustor according to athird embodiment of this invention. The gas turbine combustor accordingto this embodiment has a plurality of premix nozzles arranged on pitchcircles D₁ and D₂ (D₁>D₂) which exist on a plane perpendicular to theaxial direction of the combustor inner cylinder 20 and which differ inmagnitude from each other.

[0056] As shown in FIG. 11, in the gas turbine combustor according tothis embodiment, the diffusion flame formation cone 30 which formsdiffused combustion flames is provided inside of the combustor innercylinder 20 and a plurality of premixed flame formation nozzles (notshown) are arranged on at least two pitch circles having differentmagnitudes around this diffusion flame formation cone 30. Four premixedflame formation nozzles are arranged on each of the pitch circles D₁ andD₂. It is noted that the number of premixed flame formation nozzles isnot limited to four.

[0057] Each of the premixed flame formation nozzles has a main fuelsupply nozzle which ejects main fuel, provided therein. In addition, aswirler is provided on the air intake port side of each of the premixedflame formation nozzles. Combustion air is given turning by this swirlerand sufficiently mixed with the main fuel. Further, a nozzle extensiontube 450 is provided on the outlet side of each premixed flame formationnozzle to eject gas formed by mixing the combustion compressed air withthe main fuel, toward a combustion chamber (not shown). The outlet ofeach nozzle extension tube 450 is circular-shaped and inclined outwardin the diameter direction of the combustor inner cylinder 20. At thesame time, the nozzle extension tube 450 is inclined in the peripheraldirection of the combustion inner cylinder 20.

[0058] Premixed gas ejected from the premixed flame formation nozzles isejected toward the combustion chamber through the nozzle extension tubes450, respectively. The premixed gas ejected toward the combustionchamber is transformed to outward turning flows by the nozzle extensiontubes 450 and pass spirally within the combustion chamber. In the gasturbine combustor according to this embodiment, since the premixed flameformation nozzles are arranged on each of the two pitch circles D₁ andD₂, outward turning flows corresponding to the respective premixed flameformation nozzle groups provided on the pitch circles D₁ and D₂ aregenerated. These two outward turning flows cause circulating flows to begenerated between the neighborhood of the inner wall of the combustionchamber and the neighborhood of the center thereof and between theoutward turning flows formed by the outside premixed flame formationnozzle group and the outward turning flows formed by the inside premixedflame formation nozzle group, respectively, thereby sufficiently mixingthe premixed gas. As a result, local high-temperature portions arereduced and the generation of NO_(x) can be suppressed. In addition, thetwo recycle regions make the premixed flames more stable to make itpossible to reduce oscillating combustion and the like.

[0059] Furthermore, in the gas turbine combustor according to thisembodiment, since the premixed flame formation nozzles are arranged oneach of the two pitch circles D₁ and D₂, it is possible to appropriatelyselect premixed flame formation nozzle groups to be used according toload. Therefore, it is possible to perform a rarefied combustionoperation at an optimum fuel-to-air ratio with partial load through fullload, making it possible to suppress the generation of NO_(x) in allload regions.

[0060]FIG. 12 is a front view of a gas turbine combustor according to afourth embodiment of this invention. FIG. 13 is a cross-sectional viewof a nozzle extension tube used in the gas turbine combustor accordingto the fourth embodiment, taken along an axial direction thereof. Thisgas turbine combustor adjusts the direction of premixed gas by finsprovided inside of nozzle extension tubes 460.

[0061] The gas turbine combustor according to this embodiment differsfrom the gas turbine combustor according to the first embodiment in thatthe fins inclined in a certain direction are used as one of units whichform outward turning flows. As shown in FIG. 12 and FIG. 13, the outletof each of the nozzle extension tubes 460 is inclined toward the innerwall of the combustor inner cylinder 20 and this inclination gives anoutward flow to the premixed gas. In addition, fins 465 each of whichgives the premixed gas turning in the peripheral direction of thecombustor inner cylinder 20 are provided in the neighborhood of theoutlet of the nozzle extension tube 460. The number of fins 465 can beappropriately changed. It is noted that the fins 465 may be attached tothe inner wall of the combustor inner cylinder 20. In this case, thefins 465 are disposed closer to a combustion chamber (not shown) andexposed to high temperature. Therefore, it is preferable that the fins465 are cooled by a cooling unit such as a film cooling unit or aconvection cooling unit.

[0062] In the gas turbine combustor according to this embodiment, thefins 465 are provided at the outlet of each nozzle extension tubes 460and the outlet of each nozzle extension tube 460 is inclined outward inthe diameter direction of the combustor inner cylinder 20. Therefore,the premixed gas ejected from the nozzle extension tubes 460 istransformed to flows traveling spirally around the axis of the combustorinner cylinder 20, so-called outward turning flows. The outward turningflows allow the premixed gas to be sufficiently mixed, thereby making itpossible to reduce local high-temperature portions and to suppress thegeneration of NO_(x). Further, pressure is high in the neighborhood ofthe inner wall of the combustion chamber 50 and low in the neighborhoodof the center thereof because of the outward turning flows. As a result,a large circulating flow is generated between the neighborhood of theinner wall of the combustion chamber 50 and the neighborhood of thecenter thereof to widen a recycle region. This stabilizes the combustionof the premixed gas. It is noted that the same advantage can be attainedif the fins 465 are attached to the inner wall of the combustion innercylinder 20.

[0063]FIG. 14 is a front view of a gas turbine combustor according to amodification of the fourth embodiment. FIG. 15 is a cross-sectional viewof a premixed flame formation nozzle extension tube used in the fourthembodiment, taken along an axial direction thereof. The above-stated gasturbine combustor gives turning to the premixed gas by the fins 465, butthe gas turbine combustor according to this modification gives outwardflows to premixed gas by fins 475 and turning thereto by inclining eachnozzle extension tube.

[0064] In the gas turbine combustor according to this modification, thefins 475 are provided at the outlet of each nozzle extension tube 470,and the outlet of each nozzle extension tube 470 is inclined so as togive turning to the premixed gas in the peripheral direction of thecombustor inner cylinder 20. In addition, the fins 475 are inclinedoutward in the diameter direction of the combustor inner cylinder 20 tothereby give flows in the diameter direction thereof to the premixedgas. It is noted that the number of the fins 475 can be appropriatelychanged.

[0065] The premixed gas ejected from the nozzle extension tubes 470 istransformed to flows traveling spirally around the axis of the combustorinner cylinder 20, i.e., outward turning flows by the inclination of thenozzle extension tube 470 and the fins 475. The outward turning flowscause the premixed gas to be sufficiently mixed, making it possible toreduce local high-temperature portions and to suppress the generation ofNO_(x). Further, pressure is high in the neighborhood of the inner wallof a combustion chamber 50 and low in the neighborhood of the centerthereof by the outward turning flows. As a result, a circulating flow isgenerated between the inner wall of the combustion chamber 50 and thecenter thereof to widen a recycle region. Since this recycle regionbecomes larger than that when the premixed gas forms inward turningflows, premixed flames are formed in a stable manner. As a result,oscillating combustion and the like are decreased, making it possible toperform operation more stably than the conventional combustor.

[0066] According to the gas turbine combustor as one aspect of thisinvention, the premixed flame formation nozzle extension section whichforms a flow of premixed gas turning in a peripheral direction of thecombustor inner cylinder while being directing outward in a diameterdirection of the combustor inner cylinder is provided at the outlet ofthe premixed flame formation nozzle which forms premixed flames out ofpremixed gas formed by mixing the main fuel with the air. Since thispremixed flame formation nozzle extension section gives the premixed gasa flow directing toward the inner wall surface of the combustor innercylinder and turning, the premixed gas is sufficiently mixed in theprocess of flowing spirally around the diffusion flames. Because of thismixing action, local high-temperature portions are hardly generated andthe generation of NO_(x) can be sufficiently suppressed. In addition,since a recycle region formed in the neighborhood of the center of thecombustor is widened, the premixed flames are stably formed and stableoperation can be performed.

[0067] According to the gas turbine combustor of another aspect of thisinvention, the premixed flame formation nozzle extension section isinclined outward in the diameter direction of the combustor innercylinder and in the peripheral direction thereof with respect to theaxial direction of the combustor inner cylinder so as to give premixedgas a flow directing toward the inner wall surface of the combustorinner cylinder and turning. Therefore, the premixed gas ejected fromthis premixed flame formation nozzle extension section is sufficientlymixed and the combustion of the premixed gas evenly, sufficientlyprogresses over the axial direction of the combustion chamber in theprocess of flowing outward and spirally within the combustor chamber.Because of this action, local high-temperature portions are hardlygenerated and the generation of NO_(x) can be sufficiently suppressed.Further, since a recycle region formed in the neighborhood of the centerof the combustion chamber is widened, premixed flames are stably formedand stable operation can be performed. Furthermore, because of thesimple structure of inclining the outlet of the premixed flame formationnozzle extension section, the gas turbine combust or can be easilymanufactured and the durability thereof improves.

[0068] According to the gas turbine combustor of still another aspect ofthis invention, mixed gas and premixed gas of the pilot fuel and thecompressed air are formed in the mixed gas formation cylinder and areejected from the mixed gas ejection extension section inclined outwardin the diameter direction of the combustor inner cylinder and in theperipheral direction thereof with respect to the axial direction of thecombustor inner cylinder. Therefore, the premixed gas and the mixed gasbecome outward turning flows and pass spirally within the combustionchamber. Therefore, pressure is high in the neighborhood of the innerwall of the combustion chamber and low in the neighborhood of the centerthereof. As a result, the combustion of the premixed gas progresseswhile the premixed gas is being sufficiently mixed. Therefore, localhigh-temperature portions are reduced and the generation of NO_(x) canbe sufficiently suppressed. In addition, since a recycle region formedbetween the neighborhood of the inner wall of the combustion chamber andthe neighborhood of the center thereof is widened to thereby stabilizeflames and suppress oscillating combustion and the like, making itpossible to perform stable operation.

[0069] Furthermore, the combust or inner cylinder cooling unit isprovided on a portion on which at least premixed flames formed by thepremixed flame formation nozzle or flames formed by the gas ejected fromthe mixed gas formation cylinder are struck against an inner peripheryof the combustor inner cylinder. Therefore, it is possible to suppressthe temperature of the combustor inner cylinder from rising. It is thuspossible to create an outward turning flow more actively withoutshortening the life of the combustor inner cylinder. As a result, it ispossible to sufficiently suppress the generation of NO_(x). In addition,since it is possible to further widen a recycle region, it is possibleto ensure more stable operation.

[0070] Although the invention has been described with respect to aspecific embodiment for a complete and clear disclosure, the appendedclaims are not to be thus limited but are to be construed as embodyingall modifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

What is claimed is:
 1. A gas turbine combustor comprising: a combustorinner cylinder; a diffusion flame formation cone which is disposedinside of the combustor inner cylinder and which forms diffusion flamesby mixing pilot fuel with air; a premixed flame formation nozzle whichis provided annularly between the combustor inner cylinder and a pilotflame formation cone and which forms premixed flames out of premixed gasformed by mixing main fuel with the air; and a premixed flame formationnozzle extension section which is disposed at an outlet of the premixedflame formation nozzle and which forms a flow of premixed gas turning ina peripheral direction of the combustor inner cylinder while beingdirecting outward in a diameter direction of the combustor innercylinder.
 2. The gas turbine combustor according to claim 1 furthercomprising a combustor inner cylinder cooling unit which is provided ona portion on which at least premixed flames formed by the premixed flameformation nozzle or flames formed by the gas ejected from the mixed gasformation cylinder are struck against an inner periphery of thecombustor inner cylinder.
 3. A gas turbine combustor comprising: acombustor inner cylinder; a diffusion flame formation cone which isdisposed inside of the combustor inner cylinder and which formsdiffusion flames by mixing pilot fuel with air; a premixed flameformation nozzle which is provided annularly between the combustor innercylinder and a pilot flame formation cone and which forms premixedflames out of premixed gas formed by mixing main fuel with the air; anda premixed flame formation nozzle extension section which is disposed atan outlet of the premixed flame formation nozzle while being inclinedoutward in a diameter direction of the combustor inner cylinder and in aperipheral direction of the combustor inner cylinder with respect to anaxial direction of the combustor inner cylinder, and which ejectspremixed gas formed at the premixed flame formation nozzle.
 4. The gasturbine combustor according to claim 3, further comprising a combustorinner cylinder cooling unit which is provided on a portion on which atleast premixed flames formed by the premixed flame formation nozzle orflames formed by the gas ejected from the mixed gas formation cylinderare struck against an inner periphery of the combustor inner cylinder.5. A gas turbine combustor comprising: a combustor inner cylinder; amixed gas formation cylinder which has a nozzle ejecting pilot fuel anda nozzle ejecting main fuel, and which is disposed inside of the mixedgas formation cylinder; and a mixed gas ejection extension section whichis disposed at an outlet of the mixed gas formation cylinder while beinginclined outward in a diameter direction of the combustor inner cylinderand in a peripheral direction of the combustor inner cylinder withrespect to an axial direction of the combustor inner cylinder, and whichejects gas formed by mixing the pilot fuel with air and premixed gasformed by mixing the main fuel with the air.
 6. The gas turbinecombustor according to claim 5, further comprising a combustor innercylinder cooling unit which is provided on a portion on which at leastpremixed flames formed by the premixed flame formation nozzle or flamesformed by the gas ejected from the mixed gas formation cylinder arestruck against an inner periphery of the combustor inner cylinder.